JP2013509851A - A method of charging or discharging a battery for determining the end of charging or discharging based on current and temperature measurements - Google Patents

Abstract

The method for charging or discharging the battery (1) includes a step of measuring a voltage (U _b ) at a terminal of the battery and a step of comparing the measured voltage (U _b ) with a voltage threshold value at the end of charging or discharging. Including. The method also includes measuring a temperature (T _b ) representing the temperature of the battery and measuring a current (I _b ) flowing through the battery (1) to form a measurement pair. The voltage threshold is then determined by the measured value pair. Battery charging or discharging is stopped when the voltage threshold is reached.

Description

  The present invention relates to a method for charging or discharging a battery.

  In order to optimize battery operation, it has been necessary to develop regulators that are responsible for managing different charging and / or discharging methods. The development of new technologies for the use of renewable energy sources that can input power into the power system for direct use or can store the current generated in the battery for future use. It has been advanced.

  A known regulation mode is on / off regulation, which suspends charging when the voltage reaches a first high voltage disconnect (HVD) threshold, and the voltage is Based on resuming charging when a High Voltage Reconnect (HVR) threshold is reached. On / off type adjustment is often used in the photovoltaic field where there is generally no end-of-charge criterion. In fact, when the user uses this system, the battery is discharged at the same time as the adjustment is completed. However, if there is no action from the user and the period during which the system is not used becomes long, the battery is overcharged, which easily damages the battery.

  It is possible to determine the end of charging by fixing the maximum adjustment time. However, this standard is rarely used because the charge time for adjustment to reach full battery charge varies depending on the current rate of charge, the type of battery used, or the condition of the battery.

  However, end-of-charge management is particularly important for achieving a given charge state of the battery while limiting the electrolysis of water, especially as far as batteries with certain interfering reactions, especially water electrolytes are concerned. It is.

At the same time, the following purposes:
-Limiting battery maintenance requirements, called open batteries where water can be added to compensate for losses,
-The addition of water is not possible, ensuring the safety of sealed batteries where overcharging can lead to thermal runaway and / or explosion,
-Finally, optimization of battery life,
Therefore, limiting these interfering reactions is a major challenge.

  EP-A-1990890 describes a charging method using two charging modes controlled by a charging control unit. In the first charging mode, charging is of the control current type, and in the second charging mode, charging is of the control voltage type. In the first charging mode, the method includes a voltage threshold that is a function of temperature and charging current. When the voltage threshold is reached, the control unit changes its behavior and charging is detected if the end of charge is detected and a rapid temperature rise of the battery occurs or if the charge current value reaches a predetermined threshold. Stop.

European Patent Application No. 1990890

  It is an object of the present invention to perform battery charging or discharging by stopping charging or discharging in a timely manner so as to optimize battery life.

This object is achieved by the appended claims, and more particularly the following steps:
-Measuring the voltage at the battery terminals;
-Measuring a temperature representative of the temperature of the battery and determining a voltage threshold for end of charge or end of discharge according to a pair of measurements formed by measuring the current flowing through the battery;
-Comparing the measured voltage with the end-of-charge or end-of-discharge voltage threshold;
-Stopping charging or discharging when a voltage threshold is reached;
Achieved by a method comprising:

  Other advantages and features will be more apparent from the following description of specific embodiments of the invention given for non-restrictive illustrative purposes only and represented in the accompanying drawings.

It is a figure showing an example of a stand-alone system. It is a figure showing the three-dimensional mapping showing the relationship between the voltage threshold value showing a charge state of 80%, a charging current, and temperature. It is a figure showing the three-dimensional mapping showing the relationship between the voltage threshold value which represents a charge state of 30%, a charging current, and temperature. It is a figure showing the plot which shows the relationship between the voltage fluctuation of a battery with respect to different charging current values in predetermined | prescribed temperature, and a charging state. It is a determination flowchart incorporated in the charge and discharge regulator of a battery.

  As shown in FIG. 1, a stand-alone system generally comprises a renewable energy source connected to a battery 1. The battery 1 is recharged by a renewable energy source that can be of the solar, wind, hydraulic or geothermal type. By definition, renewable energy sources do not depend on the sustainability of service delivery, i.e. do not generate current at a constant rate. This non-constancy invalidates the use of conventional charging and discharging methods. In FIG. 1, the battery 1 is recharged by at least one solar panel 2, in other words, simply being covered with a cloud, the intensity of the charging current is reduced, or in some cases the conditions of sunlight are If it is not very favorable, the battery charge may be interrupted.

  Thus, the charge or discharge characteristics of the battery can vary depending on the charge / discharge state and the temperature of the battery 1. Therefore, when charging is performed depending on a renewable energy source, it is difficult to determine the moment when charging is stopped. Similarly, in order to prevent the battery from deteriorating, it is preferable not to discharge the battery too heavily, but the same charging principle applies to the discharging of the battery 1 as well.

  The methods described below are particularly suitable for batteries connected to renewable energy sources, but can be adapted to fit any type of battery connected to various current sources.

Thus, the charging or discharging process of it is preferably a battery 1 connected to a renewable energy source 2, the steps of at least measuring the voltage U _b of the battery 1 terminal, charge termination or discharge a measured voltage U _b Comparing to an end voltage threshold. The method further includes measuring a temperature T _b representative of the temperature of the battery 1 and measuring a current I _b flowing through the battery, thus forming a pair of measured values (T _b , I _b ). . By convention, if the current is negative, the battery is discharged, and if positive, it is recharged. Voltage threshold is determined according to a pair of measurements is formed by measurement of the measurement and the current I _b of the temperature T _b. In fact, voltage threshold, depending on the use conditions, i.e., in response to the charging current or the respective discharge currents, and may vary according to the temperature T _b of the battery 1. Next, the voltage threshold value determined from the pair of measurement values can be corrected while finely adjusting the charge end or discharge end reference.

  When the measured voltage Ub reaches the voltage threshold value, charging or discharging of the battery is stopped. Stopping means that the battery charging or discharging end criterion has been reached. In this case, charging is not resumed until the measured voltage falls below the voltage threshold. Similarly, once the end of discharge criterion is reached, the discharge is not resumed as long as the measured voltage remains below the voltage threshold.

  The measured current Ib is either an instantaneous current or an average value of currents measured over a predetermined time.

It is preferable that the voltage U _{b at} the terminal of the battery 1, the current I _b flowing through the battery, and the temperature T _b of the battery 1 are measured simultaneously. By this measurement, an accurate image of the charge or discharge characteristics at the time of measurement can be obtained.

  Various measurements are preferably made periodically to recognize the nature of the battery at regular intervals and stop charging or discharging as soon as the end of charge or discharge threshold is reached.

  According to a development, the voltage threshold corresponds, for example, to the threshold of the state of charge according to the battery type. Thus, during discharging, the threshold can be selected to prevent heavy discharge of the battery, and during charging, the threshold can be selected to prevent problematic chemical reactions due to excessive charging.

  In order to prevent damage to the battery, the voltage threshold depending on the current and the measured temperature preferably corresponds to a value representing the state of charge of the battery between 20% and 30%. This threshold can protect the battery from degradation such as sulfation of the lead acid battery or metal lithium deposition of the lithium battery, and can maintain the minimum available power in the battery. It is preferable that the voltage threshold value corresponding to the charge termination standard corresponds to a value representing a charged state of the battery of 75% to 90%. The 75% state of charge limits lead-acid battery degassing, 80% extends the life of LiMH batteries, and 90% eliminates the need to balance the different elements of the battery when the battery is made of lithium. In other words, the voltage threshold value determined by measuring the current Ib and the temperature Tb can represent the state of charge of the battery, that is, the physical state. By stopping charging or discharging in a timely manner, battery integrity can be preserved over time.

  If the battery remains constant between these charge and discharge thresholds, the interfering chemical reaction is greatly reduced and the long-term independence of the battery is greatly improved.

  The state of charge generally corresponds to a battery indicator expressed as a percentage. The battery is considered empty when 0% and fully charged when 100%. Typically, the state of charge varies depending on the amount of current stored in the battery relative to the nominal rated capacity of the battery.

In other words, in order to stop charging or discharging in a timely manner, a voltage threshold associated with a pair of measured values, that is, a measured value obtained by measuring the temperature T _b and measuring the current I _b flowing through the battery 1 is determined. Preferably, the determination of the voltage threshold is performed by selecting from a predetermined set of measurement pairs. In this way, charging and discharging termination criteria are fine-tuned to preserve battery integrity as much as possible. For this reason, the voltage threshold value is preferably supplied from a table of voltage values. Next, the table may include two inputs, the first input indicating the current value and the second input indicating the temperature value. If the measured value of the temperature T _b and the current I _b does not correspond to a known pair, i.e., closest to these two values if no voltage value obtained from the table, that may have a voltage value in these values A pair can be selected to determine a voltage threshold corresponding to a charge termination or discharge termination criterion.

Such a table may be pre-established under conditions where all charge or discharge parameters (charge / discharge current, temperature, charge state, etc.) are determined. As a specific example, the establishment of a table involves the following steps:
The voltage U _b at the terminal of the battery 1 as a function of the state of charge of the battery 1, and a plurality of curves each established for the pair formed by the battery temperature T _b and the current I _b flowing through the battery 1 Providing steps;
-For each curve, determining a voltage value from the state of charge of the battery 1;
-Adding each voltage value thus determined to the table;
including.

  Thus, each voltage value can be obtained by fixing the first and second inputs of the table for each of the current and temperature that allowed the voltage value to be determined.

  As a specific example of the embodiment of the table, in the case of charging the battery 1, the voltage and the state of charge of the battery (1 is 100% charge) at a predetermined temperature (25 ° C. in the example of FIG. 4) A plurality of curves are established, such as the curves shown in FIG. Each curve is associated with a different charge rate (3.33A, 2A and 1A in the case of FIG. 4). The same steps are repeated for multiple different temperatures.

In order to determine the voltage value associated with the charging of the battery, the state of charge is fixed at between 75% and 90% of the battery. Therefore, the reading in FIG. 4 fixes the voltage for the current / temperature pair. For example, by fixing the state of charge to 80% (0.8 in FIG. 4), the 25 ° C. and 1A pair is associated with a voltage value of approximately 3.825V. Thus, when the charging method is performed, if the measured values T _b and I _b are equal to 25 ° C. and 1 A, respectively, the table reading gives exactly 3.825 V as the voltage threshold.

  For the establishment of the pair set associated with the discharge, the curve of FIG. 4 is again plotted from the charged battery for different discharge currents. Next, the state of charge is fixed at a state of charge of 20% to 30% of the battery.

According to a particular embodiment, any measurement of the temperature T _b and the charging or discharging current I _b of the battery 1, it is possible to correspond to a predetermined voltage threshold. Thus, if the temperature T _b of the battery varies in a first predetermined range, the temperature measurement is performed by the temperature sensor 3 for feeding a first value from the N values representing the first range . If the current I _b flowing through the battery 1 fluctuates within a second predetermined range, the measuring means 4 for feeding a second value from among the M values representing the second range, the measurement of the current I _b Executed. The table then includes N ^* M voltage values, each voltage being obtained by a single pair of temperature and current formed by the first and second values. In other words, each of the temperature sensor 3 and the current measuring means 4 has a predetermined resolution capable of measuring a certain number of values within a predetermined range.

  As a specific example illustrating the embodiment described above, the first range corresponds to an interval between 0 ° C. and 60 ° C., and outside that range is considered to cause damage to the interior of the battery, so Use is not allowed. The resolution of the temperature sensor is 1 ° C., and the resolution means the measurement accuracy of the related sensor. If the actual temperature is 1.8 ° C, the measured temperature is 2 ° C. According to this condition, the set of measurable temperatures represents a set N of 61 values. In the same principle, in the case of the current measuring means 4 having a resolution of 0.01 A over the range of 0 A to 2 A representing the current that can be supplied by the renewable energy source 2 during charging, the current measuring range is the range [0.01. 2] and represents a set N of 200 different current values that can be measured by the current measuring means 4.

  Thus, ultimately, 12,200 pairs are obtained that cover all possible measurement combinations (ie, 12,200 voltage values are stored in the table).

The above table then extrapolates the fixed pair when the curve is established to finally obtain a set of N ^* M different pairs representing all measurable possibilities at the output. It can be completed by the determined pair. Preferably, in order to enhance extrapolation and to be as accurate as possible, the first range boundary and the second range boundary form part of a fixed pair to establish a curve.

  Preferably, each temperature value in the first range is separated from at least one other temperature value in the first range by a temperature difference that is less than or equal to the measurement accuracy of the temperature sensor 3, so that the number of pairs can be determined, Each current value in the second range is separated from at least one other current value in the second range by a current difference that is less than or equal to the measurement accuracy of the measuring means 4.

  Possible representations of the set of pairs are given in the form of a matrix with M rows and N columns. Each row corresponds to a different current that can be measured by the current measuring means 4 according to the resolution, and each column corresponds to a different temperature that can be measured by the temperature sensor 3 according to the resolution.

In this way, the three-dimensional mapping of FIGS. 2 and 3 can be established. FIG. 2 shows the relationship between the set of voltage values U _threshold associated with 80% state of charge, current I and temperature T. FIG. 3 shows the relationship between the set of voltage values U _threshold associated with 30% state of charge, current I and temperature T.

  Another possible indication may be a database with three fields (temperature, current, voltage) built into the battery charge and discharge regulator, the only basic of which is the temperature and current values is there.

  Any other voltage value storage means that allows the desired voltage threshold to be determined quickly can also be envisaged.

  In fact, the two pairs of sets can be distinguished. The first set corresponds to the value associated with the voltage threshold representing the end-of-charge criterion, and the second set corresponds to the value associated with the voltage threshold representing the end-of-discharge criterion.

  These sets of pairs are represented as separate for the purposes of the embodiment, but the set of pairs associated with charging and the set of pairs associated with discharging are in the form of a single table. Given, the second range includes current values having a negative lower boundary and a positive upper boundary.

  Such a table to determine end-of-charge or end-of-discharge criteria allows use of the battery only in an electrochemical window that does not cause physical damage to the battery. Thereby, it can be made longer than the lifetime of a battery, maintaining the integrity of a battery. Therefore, the replacement frequency of the battery is reduced.

According to an embodiment of the method, if the measured current I _b is negative, the method is in the discharge phase, the discharge voltage U _b of the battery terminals falls below the specified voltage threshold is stopped.

According to another embodiment of the method, if it is positive measurement current I _b is, the method is in charging phase, the charging voltage U _b of the battery terminals is equal to or higher than specified voltage threshold is stopped The

  During the life of the battery, the physical and chemical values of the battery change. As a result, the measurement pairs and the voltage thresholds associated with them may differ from those already established. Thus, according to certain embodiments, it may be useful to correct the voltage threshold. In other words, for each pair of measurements, the associated voltage threshold can be corrected after a first time representing the duration of use of battery 1. Such a correction can be performed, for example, by analyzing the physical characteristics of the battery 1 between a second time before the first time and a third time after the first time.

  According to a particular development, the correction of the voltage threshold is 100% of the battery capacity between the second time before the first time and the third time after the first time. It is a function of the amount of change in the internal resistance of a charged battery. In other words, after a predetermined period of use, the recharging step of the battery 1 is carried out until it reaches 100% of the battery capacity, and the internal resistance of the battery 1 thus charged is preferably the first defined Measured at a temperature within the range. This internal resistance is then compared to the internal resistance measured under the same conditions at a time prior to a predetermined period of use. For each pair of measurements, the associated voltage threshold is then corrected according to the comparison result of the internal resistance.

  For example, if the internal resistance of the battery drops by 20% between the second time and the third time, all voltage thresholds can then be corrected by 20%.

による一般化が可能である。 The following formula,

Can be generalized.

  Where ΔV / V is the amount of change applied to the voltage threshold, ΔR / R is the measured amount of change in the internal resistance of the battery, and α is, for example, 0.8-1.2. It is an included factor.

  The internal resistance of the battery 1 can be measured by a method such as a voltage-current curve or by impedance spectroscopy. Of course, any other method available to those skilled in the art can also be used.

  The second time preferably corresponds to a measurement of the internal resistance of a new battery charged to 100% of the battery capacity.

  The specific example above describes the use of the battery's internal resistance to correct the voltage threshold. Of course, one skilled in the art can measure other physical values to correct the voltage threshold.

FIG. 5 shows an operation determination diagram of the regulator of the stand-alone system as described above according to a specific operation example. The figure includes a first step E1 in which the voltage U _b , current I _b and temperature T _b are preferably measured simultaneously. In step E2 following step E1, the operating criteria are confirmed. This operating criterion preferably corresponds to a temperature range in which the operation of the battery is permitted, for example 0 ° C to 60 ° C. Beyond this range, the temperature can cause damage to the battery by encouraging a problematic reaction to the battery. In this way, it is possible to prevent charging and discharging of the battery outside the temperature range. If the measured temperature _Tb is out of range (output “No”), the battery is stopped (step E3) and the process returns to step E1. In contrast, if the measured temperature is within the operating range of the battery (output “yes”), the regulator proceeds to step E4 where the measured current _Ib is checked. If the measured current I _b is 0A less, the regulator, the flow proceeds to E5 corresponding to checking criteria discharge end from the value of the measured current I _b and the temperature T _b at step E1. Once it reaches this discharge termination criterion, i.e., if the measured voltage U _b is below discharge voltage threshold, the discharge is stopped (Step 6), then the regulator returns to step E, otherwise, the regulator Return directly to step E1 (output “No” of E5). On the other hand, if the measured current is greater than 0 A at the level of step E4, the regulator proceeds to step E7 corresponding to checking the charge termination criterion from the values of current I _b and temperature T _b measured in step 1. If this charge termination criterion is reached, that is, if the measured voltage is greater than or equal to the charge voltage threshold, charging is stopped (step E8), after which the regulator returns to step E1, otherwise the regulator returns to step E1. Return directly to (output “NO” of step E7).

  Such a determination diagram can be incorporated into the software of a regulator that performs control of charging / discharging of the battery.

Claims (13)

A method of charging or discharging a battery,
Measuring a voltage (U _b ) at a terminal of the battery (1);
A step of determining a voltage threshold value at the end of charging or discharging based on a pair of measurement values formed by measuring a temperature (T _b ) representing the temperature of the battery and measuring a current (I _b ) flowing through the battery. When,
Comparing the measured voltage (U _b ) with the end of charge or end of discharge voltage threshold;
Stopping charging or discharging when the voltage threshold is reached;
A method comprising the steps of: The measurement of the voltage (U _b ) of the terminal of the battery (1), the current (I _b ) flowing through the battery (1), and the temperature (T _b ) of the battery (1) is performed simultaneously. The method of claim 1.   The voltage threshold corresponds to a state of charge threshold depending on the type of battery, and when charging is performed, the state of charge threshold corresponds to a state of charge of the battery between 75% and 90%. The method according to claim 1 or 2, characterized in that   The voltage threshold corresponds to a state of charge threshold depending on the type of battery, and when discharging is performed, the state of charge threshold corresponds to a battery state of 20% to 30%. The method according to claim 1 or 2, characterized in that   The voltage threshold is given by a table having two inputs, wherein the first input represents a current value and the second input represents a temperature value. The method according to one item. The table has the following steps:
The battery (1) charge state indicates the pressure (U _b ) at the terminal of the battery (1) and is formed by the battery temperature (T _b ) and the current (I _b ) flowing through the battery (1). Providing a plurality of curves, each of which is established;
For each curve, determining a voltage value from the state of charge of the battery (1);
Adding each voltage value thus determined to the table;
The method according to claim 5, wherein the method is preformed by: If the temperature (T _b ) of the battery (1) fluctuates in a first predetermined range, the temperature (T _b ) is measured by the temperature sensor (3), and N pieces representing the first range If the first value is sent out from the values of the current and the current (I _b ) flowing through the battery (1) fluctuates in the second predetermined range, the current (I _b ) is measured by the current measuring means (4 ) To deliver a second value out of M values representing the second range, the table including N ^* M voltage values. The method described in 1.   Each temperature value in the first range is separated from at least one other temperature value in the first range by a temperature difference that is less than or equal to the measurement accuracy of the temperature sensor (3), and each current in the second range 8. A method according to claim 7, characterized in that the value is separated from at least one other current value in the second range by a current difference equal to or less than the accuracy measurement of the measuring means (4). If the measured current (I _b ) is negative, the method is in the discharge phase, and the discharge is stopped when the voltage (U _b ) at the battery terminal falls below the determined voltage threshold. A method according to any one of claims 1 to 8, characterized in that If the measured current (I _b ) is positive, the method is in the charging phase, and charging is stopped when the voltage (U _b ) at the battery terminal is above the determined voltage threshold. A method according to any one of claims 1 to 8, characterized in that   11. The associated voltage threshold is corrected for each pair of measured values after a first time representing the duration of use of the battery (1). The method according to claim 1.   The correction of the voltage threshold is for the battery charged to 100% of the battery capacity between a second time before the first time and a third time after the first time. The method according to claim 11, wherein the method is a function of the amount of change in internal resistance.   The method of claim 12, wherein the second time corresponds to a measurement of the internal resistance of a new battery charged to 100% of the battery capacity.

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